Chain saws have existed for quite some time and have proven very useful in the clearing of land and harvesting of wood. One such chain saw assembly is designated as 100 and labeled as "Prior Art" in FIG. 3. The prior art assembly 100 generally includes a saw portion, a saw chain rotating portion, a saw chain translating portion, and a saw chain tension adjusting portion. The saw portion may be said to include a 0.75 pitch chain saw chain 110 (sold as part number 11BC by Oregon Cutting Systems of Portland, Oreg.) disposed about both a drive sprocket 120 and a saw bar 130, the latter extending radially away from the former.
The saw chain rotating portion may be said to include the saw portion and a means for rotating the saw chain 110 together with the drive sprocket 120 and about the saw bar 130. This rotating means is provided by a motor (not shown) having a shaft to which the drive sprocket 120 is keyed.
The saw chain translating portion may be said to include the saw portion and a means for translating the saw portion through a range of motion. This translating means is provided by a hydraulic cylinder 140 having a first end 141 connected to the frame of the saw (which coincides with the motor housing), and a second end 142 connected to a pivot arm 150. The pivot arm 150 is rotatably mounted on the motor shaft, between the motor housing and a ring plate 160. The saw bar 130 is also connected to the pivot arm 150, at a point approximately ninety degrees displaced from the second end 142 of the cylinder 140 (relative to the axis of the motor shaft). The arrangement of the pivot arm 150, the saw bar 130, and the cylinder 140 is such that actuation of the cylinder 140 causes rotation of the saw bar 130 and saw chain 110 about the motor shaft.
The saw chain tension adjusting portion may be said to include a means for moving the saw bar 130 radially relative to the drive sprocket 120. Movement of the saw bar 130 away from the drive sprocket 120 increases tension in the saw chain 110, and movement of the saw bar 130 toward the drive sprocket 120 decreases tension in the saw chain 110. This moving means is provided by slidably mounting the saw bar 130 to the pivot arm 150. In particular, a plate 170 is rigidly secured to the saw bar 130 and slidably secured to the pivot arm 150. A screw 175 is threaded through a flange 176 on the plate 170 and into contact with a bearing surface 156 on the pivot arm 150. Rotation of the screw 175 causes the plate 120 and the saw bar 130 to move radially relative to the motor shaft and hence, the drive sprocket 120.
The foregoing chain saw assembly 100 leaves room for improvement. For example, the drive sprocket 120 is secured to the shaft in such a manner that undesirable side-loads and/or excessive keyway wear may result. Also, sawdust and other debris may reach the motor relatively unobstructed and thereby interfere with its operation and/or durability. Moreover, the nature of the tension adjusting portion of the chain saw assembly 100 is both subjective and unyielding and thus, can both hinder operation and/or contribute to wear and tear of the saw and its components. In other words, there exists a need for an improved chain saw assembly, preferably one that can be "retrofitted" onto existing equipment in a manner that is relatively simple and cost effective.